reiserfs: get rid of resierfs_sync_super

This patch stops reiserfs using the VFS 'write_super()' method along with the
s_dirt flag, because they are on their way out.

The whole "superblock write-out" VFS infrastructure is served by the
'sync_supers()' kernel thread, which wakes up every 5 (by default) seconds and
writes out all dirty superblock using the '->write_super()' call-back. But the
problem with this thread is that it wastes power by waking up the system every
5 seconds, even if there are no diry superblocks, or there are no client
file-systems which would need this (e.g., btrfs does not use
'->write_super()'). So we want to kill it completely and thus, we need to make
file-systems to stop using the '->write_super()' VFS service, and then remove
it together with the kernel thread.

Signed-off-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/reiserfs/journal.c

···
 	 * the workqueue job (flush_async_commit) needs this lock
 	 */
 	reiserfs_write_unlock(sb);
+
+	cancel_delayed_work_sync(&REISERFS_SB(sb)->old_work);
 	flush_workqueue(commit_wq);
 
 	if (!reiserfs_mounted_fs_count) {
···
 		journal->j_first = cn;
 		journal->j_last = cn;
 	}
-	sb->s_dirt = 1;
+	reiserfs_schedule_old_flush(sb);
 	return 0;
 }
 
···
 	 ** it tells us if we should continue with the journal_end, or just return
 	 */
 	if (!check_journal_end(th, sb, nblocks, flags)) {
-		sb->s_dirt = 1;
+		reiserfs_schedule_old_flush(sb);
 		wake_queued_writers(sb);
 		reiserfs_async_progress_wait(sb);
 		goto out;

fs/reiserfs/reiserfs.h

···
 	struct dentry *priv_root;	/* root of /.reiserfs_priv */
 	struct dentry *xattr_root;	/* root of /.reiserfs_priv/xattrs */
 	int j_errno;
+
+	int work_queued;              /* non-zero delayed work is queued */
+	struct delayed_work old_work; /* old transactions flush delayed work */
+	spinlock_t old_work_lock;     /* protects old_work and work_queued */
+
 #ifdef CONFIG_QUOTA
 	char *s_qf_names[MAXQUOTAS];
 	int s_jquota_fmt;
···
 int reiserfs_allocate_list_bitmaps(struct super_block *s,
 				   struct reiserfs_list_bitmap *, unsigned int);
 
+void reiserfs_schedule_old_flush(struct super_block *s);
 void add_save_link(struct reiserfs_transaction_handle *th,
 		   struct inode *inode, int truncate);
 int remove_save_link(struct inode *inode, int truncate);

fs/reiserfs/super.c

···
 	if (!journal_begin(&th, s, 1))
 		if (!journal_end_sync(&th, s, 1))
 			reiserfs_flush_old_commits(s);
-	s->s_dirt = 0;	/* Even if it's not true.
-			 * We'll loop forever in sync_supers otherwise */
 	reiserfs_write_unlock(s);
 	return 0;
 }
 
-static void reiserfs_write_super(struct super_block *s)
+static void flush_old_commits(struct work_struct *work)
 {
+	struct reiserfs_sb_info *sbi;
+	struct super_block *s;
+
+	sbi = container_of(work, struct reiserfs_sb_info, old_work.work);
+	s = sbi->s_journal->j_work_sb;
+
+	spin_lock(&sbi->old_work_lock);
+	sbi->work_queued = 0;
+	spin_unlock(&sbi->old_work_lock);
+
 	reiserfs_sync_fs(s, 1);
+}
+
+void reiserfs_schedule_old_flush(struct super_block *s)
+{
+	struct reiserfs_sb_info *sbi = REISERFS_SB(s);
+	unsigned long delay;
+
+	if (s->s_flags & MS_RDONLY)
+		return;
+
+	spin_lock(&sbi->old_work_lock);
+	if (!sbi->work_queued) {
+		delay = msecs_to_jiffies(dirty_writeback_interval * 10);
+		queue_delayed_work(system_long_wq, &sbi->old_work, delay);
+		sbi->work_queued = 1;
+	}
+	spin_unlock(&sbi->old_work_lock);
+}
+
+static void cancel_old_flush(struct super_block *s)
+{
+	struct reiserfs_sb_info *sbi = REISERFS_SB(s);
+
+	cancel_delayed_work_sync(&REISERFS_SB(s)->old_work);
+	spin_lock(&sbi->old_work_lock);
+	sbi->work_queued = 0;
+	spin_unlock(&sbi->old_work_lock);
 }
 
 static int reiserfs_freeze(struct super_block *s)
 {
 	struct reiserfs_transaction_handle th;
+
+	cancel_old_flush(s);
+
 	reiserfs_write_lock(s);
 	if (!(s->s_flags & MS_RDONLY)) {
 		int err = journal_begin(&th, s, 1);
···
 			journal_end_sync(&th, s, 1);
 		}
 	}
-	s->s_dirt = 0;
 	reiserfs_write_unlock(s);
 	return 0;
 }
···
 
 	reiserfs_write_lock(s);
 
-	if (s->s_dirt)
-		reiserfs_write_super(s);
-
 	/* change file system state to current state if it was mounted with read-write permissions */
 	if (!(s->s_flags & MS_RDONLY)) {
 		if (!journal_begin(&th, s, 10)) {
···
 	.dirty_inode = reiserfs_dirty_inode,
 	.evict_inode = reiserfs_evict_inode,
 	.put_super = reiserfs_put_super,
-	.write_super = reiserfs_write_super,
 	.sync_fs = reiserfs_sync_fs,
 	.freeze_fs = reiserfs_freeze,
 	.unfreeze_fs = reiserfs_unfreeze,
···
 	err = journal_end(&th, s, 10);
 	if (err)
 		goto out_err;
-	s->s_dirt = 0;
 
 	if (!(*mount_flags & MS_RDONLY)) {
 		dquot_resume(s, -1);
···
 	/* setup default block allocator options */
 	reiserfs_init_alloc_options(s);
 
+	spin_lock_init(&sbi->old_work_lock);
+	INIT_DELAYED_WORK(&sbi->old_work, flush_old_commits);
 	mutex_init(&sbi->lock);
 	sbi->lock_depth = -1;
 
···
 		journal_release_error(NULL, s);
 		reiserfs_write_unlock(s);
 	}
+
+	cancel_delayed_work_sync(&REISERFS_SB(s)->old_work);
 
 	reiserfs_free_bitmap_cache(s);
 	if (SB_BUFFER_WITH_SB(s))